Device for converting a rotary motion into a linear motion

ABSTRACT

The invention is a device ( 1, 100, 200, 300, 400, 500, 600, 700 ) for converting a rotary motion into a linear motion, comprising a first threaded element ( 3 ) that defines a first axis ( 7 ), suited to be coupled with a second threaded element ( 4 ) defining a second axis ( 10 ), said axes ( 7, 10 ) being substantially parallel to each other but not coinciding with each other. The device ( 1 ) also comprises means ( 12 ) arranged between the first threaded element ( 3 ) and the second threaded element ( 4 ), suited to transmit the rotary motion imparted to one of the elements ( 3, 4 ) to the other.

The present invention concerns a device that makes it possible to intervene indirectly on the operation or control of mechanical movements.

In particular, the present invention concerns a device for converting a rotary motion into a linear motion, particularly suited to be used for moving mechanical parts.

More particularly, the present invention concerns a linear actuator where the advance for screw turn differs from the thread pitch, which can be used as an alternative to the actuators of the type currently on the market to set in motion mechanical parts like for example gates or doors. The actuator that is the subject of the invention is also suitable for equipping lifting devices like for example jacks, etc.

Some devices of known type for converting a rotary motion into a linear motion substantially comprise a support element on which a first threaded female element is rotantingly installed, said female element being coupled to a second threaded male element.

The first element is constituted by a nut screw mounted on bearings and free to rotate on a first axis.

The second element is constituted by a screw whose diameter is shorter than the diameter of the nut screw, mounted on bearings, too, which defines a second axis that is parallel to but does not coincide with said first axis.

The actuator device also comprises power means, generally consisting of an electric motor that allows the screw to be set rotating around the second axis.

In practice, the activation of the power means sets the screw rotating and this, according to the direction of rotation and to the rpm, causes a corresponding axial translation along said first axis of the nut screw and the support.

In ideal conditions, the axial translation of the support element, with the same number of screw turns, is a function of the ratio of the diameters of the two elements (screw-nut screw), as well as of the pitch of the corresponding threads.

A known drawback of these devices lies in that the ratio between the number of screw turns and the axial translation of the support is not constant but varies depending on the operating conditions of the device itself.

More precisely, the behaviour of the device depends on the friction force present between the threads of the two coupled elements at the moment of operation of the device, which varies depending on the load conditions.

In fact, when the friction developed between the two coupled threads is below a given value, the nut screw is not set rotating by the screw, as desired, and therefore does not rotate around the first axis. This means that with the same rotation of the screw the axial translation of the support is not a function of the ratio of the two diameters (screw-nut screw) of the device, but corresponds to the pitch of the two coupled threads.

This causes an undesired behaviour of the device, which makes it unsuitable for applications that require uniform behaviour in any operation mode.

More particularly, said undesired behaviour takes place when the device is idle and more precisely when the friction developed between the threads due to the contact of the two elements is not sufficient to overcome the torque generated for example by the friction of the support bearings and/or by the inertia of the elements themselves.

A first drawback posed by the devices of known type is thus constituted by the fact that they do not make it possible to guarantee a uniform linear displacement, proportional to the number of turns imparted to the screw, in any operating condition of the device. More particularly, the above mentioned drawback causes an irregular linear translation speed of the device's support when, for example, the axial load it bears is below a minimum value.

A further drawback lies in that said minimum value is typical of each device and varies over time.

In order to overcome the drawbacks mentioned above, the known art has proposed devices that fix the transmission ratio between screw and nut screw through a gear system or a timing belt system.

Said devices, though solving the problem of maintaining a regular advance motion also in the absence of external loads on the actuator, pose some drawbacks.

More particularly, a first drawback of these devices is constituted by the fact that they are complicated to carry out and require precise mechanical machining operations that considerably affect also the cost of the device itself.

A further drawback is represented by the fact that the synchronisation device increases the noise produced by the device during operation.

According to a further kind of devices of known type, the device comprises an elastic system, called preload system, that pushes the screw against the nut screw, thus guaranteeing minimum friction between the coupled threads.

A first drawback posed by said devices is constituted by the fact that they offer a low level of efficiency, determined by the force exerted on the threads by the elastic element.

A further drawback is constituted by the fact that the force generated by the elastic element acts continuously and directly on the coupled threads, thus increasing their wear over time. This causes slacks and mechanical malfunctions, as well as further reducing the efficiency of the device.

A further drawback posed by said devices lies in that they are not reliable and present malfunctions especially when the axial direction in which the support moves corresponds to the force exerted by the load to be moved.

The aim of the present invention is to overcome the drawbacks described above.

In particular, it is a first aim of the invention to construct a device for converting a rotary motion into a linear motion that makes it possible to guarantee a uniform linear displacement, proportional to the number of screw turns and independent of the conditions of use.

More particularly, it is one aim of the invention to construct a device whose linear advance speed is uniform, dependent on the number of turns imparted to the screw and independent of the load applied to the device.

It is a further aim of the invention to carry out a device offering high efficiency in terms of operating torque applied and linear displacement obtained, that is, allowing substantially all the torque applied to the screw to be used to obtain the desired linear displacement.

It is another aim of the invention to carry out a reversible device, that is, a device capable of working when the screw is set rotating with idle nut screw, or when the nut screw is set rotating with idle screw, or when the support element is set rotating and the screw rotation is locked.

It is a further aim of the invention to carry out a device that ensures sufficiently precise and fine control of the linear advance obtained, independently of the load applied.

It is another aim of the invention to obtain a device particularly suitable for making linear actuators for converting a rotary motion into a linear and preferably regular motion, that ensures sufficiently precise positioning, high efficiency and requires a low torque for operation.

It is another aim of the invention to carry out a device featuring noiseless, simple, economic and reliable synchronization between screw and nut screw, with few components and capable of ensuring widening of the actuator's field of application, the advance being regular also in the absence of external loads and therefore of friction between the threads of screw and nut screw at the contact points.

Lastly, it is a further aim of the invention to make an intrinsecally reliable and safe device that will last over time.

The aims described above have been achieved through the construction of a device for converting a rotary motion into a linear motion according to the contents of the main claim.

The proposed solution advantageously makes it possible to ensure in a simple and effective way the desired operation of the device in any condition of use, with no need for highly precise mechanical elements.

Furthermore, the proposed solution does not involve action on the coupled threads of the two elements and therefore does not affect their wear and the efficiency of the device itself.

Still advantageously, the solution proposed is easy to carry out, reliable, economic and noiseless.

Advantageous embodiments of the invention are the subject of the dependent claims.

Still advantageously, the solution proposed makes it also possible to make up for imprecise and rough mechanical processing.

The aims and advantages described above will be highlighted in greater detail in the description of some preferred embodiments of the invention, supplied as examples without limitation, with reference to the attached drawings, wherein:

FIG. 1 is a perspective view of a partial cross section of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 2 shows a longitudinal section of the device shown in FIG. 1;

FIG. 3 is an exploded view of the device shown in FIG. 1;

FIG. 4 is a perspective view of some elements of the device shown in FIG. 1;

FIG. 5 is a perspective view of some of the elements shown in FIG. 4;

FIG. 6 is a perspective view of a partial cross section of another example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 7 shows a longitudinal section of the device shown in FIG. 6;

FIG. 8 is an exploded view of the device shown in FIG. 6;

FIG. 9 is a perspective view of some elements of the device shown in FIG. 6;

FIG. 10 is a perspective view of some of the elements shown in FIG. 9;

FIG. 11 is a perspective view of a partial cross section of a further example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 12 shows a longitudinal section of the device shown in FIG. 11;

FIG. 13 is an exploded view of the device shown in FIG. 11;

FIG. 14 is a perspective view of some elements of the device shown in FIG. 11;

FIG. 15 is a perspective view of some of the elements shown in FIG. 14;

FIG. 16 is a perspective view of a partial cross section of another example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 17 shows a longitudinal section of the device shown in FIG. 16;

FIG. 18 is an exploded view of the device shown in FIG. 16;

FIG. 19 is a perspective view of some elements of the device shown in FIG. 16;

FIG. 20 is a perspective view of some of the elements shown in FIG. 19;

FIG. 21 is a perspective view of a partial cross section of a further example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 22 shows a longitudinal section of the device shown in FIG. 21;

FIG. 23 is an exploded view of the device shown in FIG. 21;

FIG. 24 is a perspective view of some elements of the device shown in FIG. 21;

FIG. 25 is a perspective view of some of the elements shown in FIG. 24;

FIG. 26 is a perspective view of a partial cross section of another example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 27 shows a longitudinal section of the device shown in FIG. 26;

FIG. 28 is an exploded view of the device shown in FIG. 26;

FIG. 29 is a perspective view of some elements of the device shown in FIG. 26;

FIG. 30 is a perspective view of some of the elements shown in FIG. 29;

FIG. 31 is a perspective view of a partial cross section of another example of embodiment of a device for converting a rotary motion into a linear motion that is the subject of the present invention;

FIG. 32 is an exploded view of the device shown in FIG. 31;

FIG. 33 is a perspective view of some elements of the device shown in FIG. 31;

FIG. 34 is a perspective view of some of the elements shown in FIG. 33;

FIG. 35 shows a longitudinal section of a further preferred embodiment of a device carried out according to the invention.

First of all it is important to point out that identical or similar components in different examples of embodiments are indicated by the same reference numbers. The position indications given in the different examples of embodiment should be transferred to the new position.

A practical embodiment of a device for converting a rotary motion into a linear motion, subject of the present invention, is shown in FIG. 1, where it is indicated as a whole by 1.

It comprises a support element 2 on which a first threaded female element 3, visible in particular in FIGS. 2 to 5, is rotatingly installed, said female element being coupled to a second threaded male element 4.

The support element 2 comprises two parts 2 a and 2 b visible in FIG. 2 and joined by screws indicated by 2 c.

The first element 3 is constituted by a nut screw 5 mounted on ball bearings 6 integral with the support 2, said nut screw being free to rotate on a first axis 7.

The second element 4 comprises a screw 8 whose thread diameter 9 is shorter that the thread diameter of the hole of the nut screw 5. The screw 8 defines a second axis 10 parallel to but not coinciding with the above mentioned first axis 7 and is guided in its axial stroke by two guide bearings 11, 11 a provided with a hole that substantially corresponds to the nominal diameter of the screw 8. In this way the screw 8 fits in the hole with a minimum slack, sufficient to allow it to rotate freely and also to slide axially. The screw 8 and the nut screw 5 are arranged eccentrically with respect to each other and maintained in said position inside the support 2 by the respective bearings, so that the threads of the screw 8 and of the nut screw 5 come into contact with each other though presenting a minimum slack, indicatively included between 0.001 and 0.3 mm, depending on the precision and size of the device. According to the invention, the device 1 also comprises means 12 arranged between the first threaded element 3 and the second threaded element 4, suited to transmit the rotary motion imparted to one of the two threaded elements 3, 4 to the other by friction.

This makes it possible to guarantee the rotation of the coupled elements 3, 4 on the thread even when the device 1 is idle, preventing any irregularity in the advance of the actuator and setting the advance per screw turn to a given value, a function of the ratio between the diameters of the screw 8 and the nut screw 5, as well as of the thread pitch of the same.

This solution guarantees that the nut screw 5 is always set rotating by the screw 8, or vice versa, also independently of the loads and the friction present in the system.

This advantageously makes it possible to guarantee a motion that is always smooth and without abrupt relative axial accelerations between screw 8 and nut screw 5 and thus between screw 8 and support 2.

In the particular embodiment of the invention illustrated in Figures from 1 to 5, said means 12 comprise an annular elastic element 13 housed in an annular seat 14 obtained in an annular support 15 mounted on the screw 8.

More precisely, the annular element 13 is mounted on the outside of the support 15 and is integral with it owing to the elastic properties of the element 13 itself.

The elastic element 13 is suited to cooperate by friction with at least one portion of a surface integral with the first element 5, comprising, in the preferred embodiment of the invention described herein, a cylindrical surface 16 obtained in the nut screw 5.

In particular, the elastic element 13 is enclosed in a seat 17 and exerts pressure against the properly shaped and unthreaded wall 16 of the nut screw 8, transmitting any relative rotation of one element 3 to the other element 4 and vice versa by friction.

As regards the support 15, it is coupled to the screw 8 in such a way as to allow it to slide axially along the axis 10 and prevent it from rotating with respect to the same axis.

More particularly, the coupling between the support 15 and the screw 8 is obtained by providing a facet 18 on the screw 8 or flattening the crest of the thread that cooperates with a portion of a plane counteracting surface 20 of the support element 15 that prevents mutual rotation between the screw 8 and the support element 15, thus allowing axial sliding.

As already explained, the support element 15 is housed in a seat 17 defined by a first counteracting surface 21 axially integral with the support element 2, constituted, in the example, by a shoulder of the nut screw 5, and by a second counteracting surface 22 that is also axially integral with the support element 2 and belongs, in the example illustrated, to the inner ring of the upper guide bearing 11 a.

The shoulder 21 and the second counteracting surface 22 act on the support element 15 moving it axially when the device 1 is activated, as will be better described below.

Alternatively, the counteracting surfaces 21 and 22 may be both obtained in the nut screw 5 or the support 2, and may be preferably rotating together with the nut screw 5 or the screw 8 to limit energy losses due to sliding friction at the same time maintaining high efficiency.

It should also be noted that the groove of the thread of the screw 8 is sufficiently deep to ensure that the above mentioned facet does not affect the bearing part of the thread.

It is clear that the annular element 13 may be made of any material resistant to wear that guarantees the transmission of motion by friction. Preferably, it is constituted by a rubber elastic ring, for example an O ring.

It is also clear that, in other embodiments, the system for preventing mutual rotation comprising the plane counteracting surface 20 and the facet 18 can be replaced by analogous means, all suited to prevent any relative rotation between the screw 8 and the support 15 and constituted, for example, by tab or tooth systems. In particular, the plane counteracting surface 20 can be replaced by any other element projecting from the inner cylindrical wall of the annular support 15, capable of counteracting any mutual rotation when it comes into contact with the facet 18.

It should also be observed that the support element 15 is coaxial with the screw 8 and therefore the elastic element 13 is transversally in contact with the nut screw only in a small area.

A further preferred embodiment of the invention indicated as a whole by 100 is shown in Figures from 6 to 10.

This embodiment is differentiated from the previous one due to the fact that the means 12 comprise a support element 15 a constituted by a substantially annular open element.

More precisely, in this embodiment the screw 8 is inserted in a ring 15 a having an opening 27 whose inner walls define a hole whose diameter is slightly shorter than the diameter of the screw 8 a that in this case has no flattening and/or facets on the thread crest. Advantageously with this solution the ring 15 a, once inserted in the screw 8 a, adapts to the diameter of the screw 8 a and exerts on it, through its inner wall, a pressure that though being within the limits of the friction force between the surfaces, makes the ring integral with the screw 8 a itself, guaranteeing at the same time its axial sliding in a way analogous to that proposed in the solution previously described.

It should also be observed that the ring 15 a advantageously has one or more parts or sectors 28 with reduced thickness.

Said areas with reduced thickness define regions of preferential yield that make it possible to increase the capacity of the ring 15 a to adapt to the diameter of the screw 8 a and thus ensure better adhesion of the element 15 a itself to the screw 8 a. This reduced thickness can be obtained, for example, with one or more cuts made on the metal ring.

It should also be noted that in this embodiment outside the support element 15 a there are several elastic rubber elements 13 a, also called O rings, of the type described above. Said elastic elements 13 a, once inserted in the metal ring and successively in the actuator, as shown in the exploded view of FIG. 8, exert a pressure against the properly shaped and unthreaded wall of the nut screw, thus generating the friction necessary to transmit rotation of the screw to the nut screw and vice versa, even when the device is idle.

It should also be observed that the elastic rings (O rings) facilitate adhesion of the inner surfaces of the support element to the screw, thus helping prevent relative rotation between the screw and the ring.

It should also be noted that any slight relative rubbing between the O ring and the nut screw does not affect the duration of the O ring or the efficiency of the actuator.

The pressure between the ring 15 a and the screw 8 a is such as to generate a sufficient torque for the transmission of rotation between screw 8 a and nut screw 5 with no load, but not to prevent axial sliding of the screw 8 a on the ring 15 a.

The energy lost due to friction during the axial sliding of the screw 8 a in the ring 15 a is practically irrelevant for the purposes of efficiency.

It is clear that also in this case the annular element may be made of any material resistant to wear that guarantees transmission of motion by friction.

A further preferred embodiment of the invention indicated as whole by 600 is shown in Figures from 31 to 34.

This embodiment is differentiated from the previous one due to the fact that the support element 15 f comprises several distinct elements 40, 41, each being a part of a sector of a circle, which when properly positioned side by side allow the surface of the screw 8 f to be substantially encircled.

A further preferred embodiment of the invention indicated as whole by 200 is shown in Figures from 11 to 15. This embodiment is differentiated from the previous one due to the fact that the means 12 comprise a substantially annular element 13 b defining a hole whose diameter is slightly shorter than the diameter of the screw 8 b.

The element 13 b is thus maintained integral with the screw 8 b owing to the friction generated by the pressure between the contacting surfaces of the ring 13 b and the screw 8 b. This force, due to the above mentioned difference in size between the diameter of the hole defined by the element 13 b and the diameter of the screw 8 b is such as to allow the support element to slide axially, though preventing its relative rotation within the limits of the torque to be transmitted.

It should also be observed that the element 13 b in this case has at least one annular projection 29, in the example divided into sectors of a circle, suited to be coupled to a corresponding groove 30 obtained on the surface 16 b of the nut screw 5 b.

A further preferred embodiment of the invention indicated as a whole by 300 is shown in Figures from 16 to 20.

This embodiment is differentiated from the previous one due to the fact that the means 12 comprise an element 13 c constituted by a small piece of sheet integral with the screw 8 c and suited to deform and adapt to the shape of a wedge-shaped annular recess 31 c obtained in one surface 16 c of the nut screw 5 c.

In this case, the small piece of sheet 13 c bends its cylindrical walls in contact with the screw 8 c, generating pressure against the screw 8 c itself and consequently sufficient friction to transmit motion.

A further preferred embodiment of the invention indicated as a whole by 400 is shown in Figures from 21 to 25.

This embodiment is differentiated from the previous one due to the fact that the means 12 comprise an annular element 13 d preferably made of rubber or another elastic material and made integral with the nut screw 5 d using a bonding agent.

A further preferred embodiment of the invention indicated as whole by 500 is shown in Figures from 26 to 30.

This embodiment is differentiated from the previous one due to the fact that the annular element 13 e integral with the nut screw 5 e is threaded inside, in such a way as to increase the friction force generated by contact with the screw 8 e. It should be observed also that in this solution the threading diameter of the element 13 e is shorter than the diameter of the screw 8 e.

This is due to the fact that the ring 13 e is made of a compressible material and is arranged in such a way as to be slightly pressed against the screw 8 e.

In this regard it must be pointed out that the threading of the element 13 e does not have the function to move the screw 8 e axially with respect to the nut screw 5 e.

In fact, this function is performed by the threading present on the nut screw 5 e that is coupled with the corresponding thread of the screw 8 e.

A further preferred embodiment of the invention not represented herein is differentiated from the previous one due to the fact that the means 12 comprise an annular element co-moulded or vulcanised on the first element 3 that performs the functions of the annular element 13.

More precisely, the co-moulded or vulcanised element has a substantially cylindrical surface that defines a hole suitable for receiving the second element 4, through which the same can slide axially.

The cylindrical surface thus faces the second element 4, which may comprise one of the screws previously described, and is suited to counteract at least one portion of it to obtain the movement described above.

A further preferred embodiment not represented herein is differentiated from the previous one due to the fact that the device also comprises means suited to adjust the friction force developed by the means 12.

According to a preferred embodiment of the invention, said adjusting means comprise a pin that is inserted between the support element and the screw, which slightly increases the diameter of the support element itself and therefore of the seat that houses the O ring.

As regards the annular element, in the preferred embodiment it comprises an O ring made of synthetic material.

The actuator device also comprises power means, not represented in the attached drawings, generally consisting of an electric motor that allows the first threaded element 3 or the second threaded element 4 to be set rotating around its own axis, thus moving the support 2 axially.

A further preferred embodiment of the invention indicated as a whole by 700 is shown in FIG. 35.

This embodiment is differentiated from the previous one due to the fact that the device comprises several threaded elements.

More precisely, in the embodiment shown, the device comprises three first threaded elements 3 and second threaded elements 4.

In particular, the first three threaded elements 3 comprise three nut screws 5 g, 5 h and 5 i with different diameters, while the two second threaded elements 4 comprise two screws 8 g and 8 h having different diameters, too.

It is clear that in other embodiments the device may comprise a different number of first and second threaded elements 3, 4.

As regards the threads mentioned above, it is clear that they may have one or more starts, and that the direction of the threading of the coupled elements 3, 4 may be the same or not, depending on the required advance pitch.

It should also be observed that the efficiency of the device increases, reducing to a minimum the lever arm of the friction forces generated between the coupled threads of screw and nut screw.

This advantageous increase in efficiency is obtained by increasing the difference in inclination between the coupling threads of the two elements 3 and 4.

It should also be noted that the efficiency of the device increases as the ratio of the diameters of the two coupled elements 3 and 4 increases, and their ratio is preferably included between 0.3 and 0.9.

It is important to observe also that in order to prevent the load from resting on the crests of the coupled threads of the two elements with consequent wear and possible damage to the same, both the female and male threads preferably feature crests with rounded edges.

It should also be noted that to obtain sufficient support from the guide bearings of the screw, the crest of the thread of the second threaded element should be preferably constituted by a cylindrical surface.

It should also be noted that the actual profile of the thread section in the area of contact between the two elements, constituted by the sides of the thread, must preferably be such as to generate, with device under load, an approximately circular contact area. This in order to obtain the minimum lever arm of the friction force compared to the relative rotation centre.

Still to advantage, in order to obtain the best possible distribution of the load between the coupled threads of the two elements 3, 4, it is preferable for the profile of the tooth to be the profile that generates a contact of the ball-ball type.

Advantageously, the proposed threading combined with the absence of internal preloads and with surface hardening make it possible to obtain the maximum efficiency of the device.

To further increase the reliability and duration of the device, according to some embodiments of the invention the two elements 3 and 4 are subjected to surface hardening treatments like for example nitriding, case hardening, quenching, etc.

Obviously, in each one of the embodiments described herein the rotation command can be given, as already said, to the first element 3 or the second element 4 or even to the support element 2 with locked rotation of the element 4, and the axial displacement can be performed by the second threaded element or by the unit comprising the first threaded element and the support.

It is also important to note that the diameter of the hole of the above mentioned annular element and/or the external diameter of the same element can be of any size, provided that it is such as to interfere with at least one of the threaded elements 3, 4.

The operation of the device for converting a rotary motion into a linear motion that is the subject of the present invention is described below with reference to the preferred embodiment of the invention illustrated in the Figures from 1 to 5, since there are no substantial differences compared to the other embodiments described.

In practice, even when the device 1 is idling, the activation of the power means not represented herein sets rotating the screw 8, for example, and this sets rotating also the support element 15 and therefore the annular element 13.

This annular element 13 sets rotating, by friction, also the nut screw 5 that starts rotating.

The tangential speeds in the points of contact between screw and nut screw are the same and therefore, due to the difference in diameter between the screw 8 and the nut screw 5, the two elements rotate at different angular speeds that, as already known, are a function of the ratio of the above mentioned diameters.

The relative rotation between screw 8 and nut screw 5 determines a mutual axial displacement between screw and nut screw, whose direction depends on the direction of rotation imparted in this case to the screw 8.

In greater detail, the axial translation of the support element 2 along the first axis, with the same number of screw turns, is a function of the ratio of the diameters of the two elements (screw-nut screw), as well as of the pitch of the corresponding threads.

By inverting the direction of rotation of the screw, the nut screw is set rotating substantially as described above and moves axially in the opposite direction.

In this way, thanks to the presence of the means 12, a sufficiently precise advance pitch is guaranteed, without irregularities and abrupt movements, independently of the external load and substantially without affecting the efficiency of the mechanism.

In greater detail, it should be noted that when the device 1 is not under load and the power means are operated, the transmission ratio is equal to the ratio between the average diameter of the element 13 and the diameter of the cylindrical contact surface 16.

When the device 1 is under load and the power means are operated, the transmission ratio is equal to the ratio between the average diameter of the screw 8 and the average diameter of the nut screw 5.

This means that if the two transmission ratios mentioned above are slightly different, this may result, with the same rotation speed of the screw, in different axial displacements between the screw 8 and the nut screw 5.

This difference in the axial displacement is however negligible.

This also makes the device insensitive to any imprecision in the size of the elements and in their coupling, which may be due for example to non-optimal mechanical machining. It is important to note that in some of the embodiments described this is facilitated by the elastic characteristics of the element 13.

This makes it possible to construct a particularly economic device, simple to carry out and suitable for many applications.

The above description clearly shows that the solution proposed allows the drawbacks described to be eliminated.

In particular, the proposed solution makes it possible to obtain an actuator device for converting a rotary motion into a substantially uniform linear motion in any load condition, with precise positioning, high efficiency and low torque required for operation.

Still advantageously, the proposed device allows linear advances to be carried out with speeds that are independent of the load and friction conditions.

Still advantageously, the proposed device allows the load that can be supported by the device to be increased even if the diameter of the screw and the nut screw remains the same as in the devices of known type, since there is no preload.

Still advantageously, the proposed device has a simple construction that means high reliability and low costs.

Still advantageously, the use of an O ring made of plastic material makes it possible to construct a device that is more silent than the known devices equipped with gear synchronization means.

Still advantageously, the proposed solution allows linear advances to be carried out at speeds that vary according to the rotation speed of the screw or nut screw, independently of the load and friction conditions.

Finally, it is important to note that advantageously the solution proposed does not require precise mechanical machining to guarantee smooth operation of the device.

Even though the invention has been described making reference to the attached drawings, upon implementation changes can be made that shall all be considered protected by the present patent, provided that they are within the scope of the inventive concept expressed in the following claims.

It is also important to remember that when the details mentioned in the claims below are followed by references, these must be understood as meant to improve the comprehensibility of the claim in question and not as a limit to the interpretation of the same. 

1-27. (canceled)
 28. A device for converting a rotary motion into a linear motion, comprising: at least a first threaded element that defines a first axis, said first threaded element being coupled with at least one second threaded element defining a second axis, said axes being parallel to each other but not coinciding with each other; and means arranged between said at least one first threaded element and said at least one second threaded element suited to transmit a rotary movement imparted to one of said elements to the other by friction, wherein said means comprise at least one annular element housed in an annular seat obtained on an annular support mounted on said at least one second threaded element.
 29. The device according to claim 28, wherein said at least one annular element is made of an elastic material.
 30. The device according to claim 28, wherein said at least one annular element is mounted on the outside of said at least one annular support.
 31. The device according to claim 30, wherein said at least one annular support is coupled to said at least one second threaded element.
 32. The device according to claim 31, wherein said at least one annular support element is coupled to said at least one second threaded element in such a way as to allow it to slide axially along said second axis and prevent mutual rotation with respect to the same axis.
 33. The device according to claim 32, wherein the mutual rotation between said support element and said at least one second threaded element is prevented by means comprising at least one facet or flattening of the thread of said at least one second threaded element that cooperates with a portion of a counteracting surface of said support element.
 34. The device according to claim 32, wherein the mutual rotation between said support element and said at least one second threaded element is prevented by means comprising tab or tooth systems or by elastic means.
 35. The device according to claim 28, wherein said at least one support element is coaxial with said at least one second threaded element.
 36. The device according to claim 28, wherein said at least one annular element is mounted inside said at least one annular support.
 37. The device according to claim 36, wherein said at least one annular element is integral with said at least one first threaded element.
 38. The device according to claim 36, wherein said at least one support element is coaxial with said at least one first threaded element.
 39. The device according to claim 28, wherein said at least one annular element is suited to cooperate by friction with at least one portion of a surface integral with said at least one first threaded element or with said at least one second threaded element.
 40. The device according to claim 28, wherein said at least one annular support element is open.
 41. The device according to claim 28, wherein the diameter of said at least one support element is such as to interfere with said at least one second threaded element.
 42. The device according to claim 28, wherein said at least one support element presents one or more preferential yield regions.
 43. The device according to claim 28, wherein said support element comprises several distinct elements each substantially defining one part of a sector of a circle.
 44. The device according to claim 28, wherein said annular element is made of an elastic material resistant to wear.
 45. The device according to claim 44, wherein said at least one annular element comprises an elastic “O” ring.
 46. The device according to claim 28, further comprising means for adjusting the friction force developed by said movement transmit means.
 47. The device according to claim 46, wherein said means for adjusting the friction force developed by said movement transmit means comprise a pin that is inserted between said at least one annular element and said at least one second threaded element or said at least one first threaded element.
 48. The device according to claim 28, wherein said at least one first threaded element is a nut screw and said at least one second threaded element is a screw.
 49. The device according to claim 28, wherein said at least one first threaded element is a screw and said at least one second threaded element is a nut screw.
 50. The device according to claim 28, further comprising a support on which said at least one first threaded element and/or said at least one second threaded element is rotatingly installed by means of bearings.
 51. The device according to claim 28, wherein said support element is housed in a seat defined by a first counteracting surface belonging to at least one of said threaded elements or integral with the inner ring of one of said bearings and by a second counteracting surface integral with the inner ring of one of said bearings.
 52. The device according to claim 28, wherein the threads of said threaded elements have one or more starts.
 53. The device according to claim 28, wherein the diameters of said threaded elements are different and their ratio is between 0.3 and 0.9.
 54. The device according to claim 28, further comprising power means suited to set said at least one first threaded element or said at least one second threaded element rotating in order to determine their mutual relative axial translation. 